Hello!
My nickname is Ma1utka, and today I want to tell you about Kog'Maw. I am not playing him a lot these days but I used to like him very much. I think, if Kog has skill and a good build he will kill everyone.
Let's begin!

Kog'Maw is a very strond ad carry, or how it can be also called ranged damage dealer. He is a very late game champion. I had a lot of games, when I didn't have lots of kills, or farm, but I destroyed everyone in late.

You can take either Heal and Flash or Ignite and Flash. 1st variant will make you more sustainly and 2nd is for more agressive Kog'Maw. I like 1st variant more.

1. Of course the best support with Kog'Maw is Nunu. Because of Blood boil(that is op in my opinion) you can strongly destroy your enemies. Because of your Bio-Arcane Barage, that take % of max. health and because of Blood Boil you have a big AS, and it let you to take lots of % of hp.
2. Also good support with Kog'maw is Zyra. Actually Zyra is pretty good with everyone. Because of her ulti and snair you can make a very good combo.
3. Sona. She will help you survive laning phase. When you pick Sona + Kog'Maw you must understand, that u will go hard late.
4. Soraka. Soraka is good just the same as Sona. If u being harassed by an opponent, Soraka will help you to come back. Also she gives you mana, so you won't be OOM.

I can't say which ADC is strong vs Kog'Maw and which is not. It depends on his and yours skill. His task is to harass you and your task is to farm more.

In laning phase you don't need to be very agressive. Your main target is to farm a lot of minions. The best creep score for you is 200 minions to 20 minute, but it is very hard to do this, so 150 to 20 minute is good too.
Lots of people begin there game with a doran's blade, but it is a big mistake. Even if you have a healer on lane you must always begin with Boots of speed and three potions. Then u better get two doran's blades to be more survival on lane. If you make a late recall or you got fed, you can also get B.F.Swordinstead of two Doran's Blades.

In Mid game Kog'Maw is stronger than in laning phase, but not as strong as in late game. In this phase you are supposed to begin team fighting. If you farmed good and didn't feed u must be winning them. In this stage we are going to take Zeal and upgrade B.F.Sword into Infinity Edge, BUT, if you are an advanced player, you can take Bloodthirster and then, in late game Infinity Edge.

In Late game you must eliminate EVERYTHING YOU SEE. I can't say anything about this phase. There is nothing special about it. If u made Laning phase and Mid game right Late game won't be difficult to you. Here we get Bloodthirster, Madred's Bloodrazor and Guardian Angel. Lots of people refuse taking Guardian Angel, because they don't see any point in it. But there is. What if you being focused in team fight? You will die. But Gurdian Angel will give you 2nd life. Advice all your team mates to take it, because it is the most awesome item in the game. You can ask me, why we don't get Last Whisper. Kog'Maw doesn't need it. His W deal magic dmg, so you would better get Guardian Angel.

Kog'Maw will deal tons of damage if you were playing him right. He is a very late game ADC.
Thank you for reading my guide!
If u have any questions about Kog'Maw, right to my email adresse: genya-sizykh@yandex.ru.
This guide will be continued.
I wish to you to win all your games. ^_^